Aft inlet ramjet powered missile

ABSTRACT

A solid fuel ramjet powered missile having the air inlets positioned adjacent the aft end of the fuel grain with a channel provided adjacent the fuel grain to provide primary air into the forward end of the fuel grain with the secondary air being supplied directly to the secondary combustor. A valve is provided in the primary air flow channel to control the air flow into the fuel grain.

6 O-'-2 5 1 SR Unlted States Patent 1 1 1 1111 3,844,118 Wilkinson Oct. 29, 1974 AFT INLET RAMJET POWERED MISSILE 3,22l,496 l2/l965 Haake 60/270 s 3,535,881 l0/l970 Schubert 60/270 S [75] lnvemor- 33: w'lk'nsom New Carhsle, 3,807,169 4/1974 Bradford 60/270 R [73] Assignee: The United States of America as Primary Examiner-Carlton R. Croyle represented by the Secretary of the Assistant ExaminerRobert E. Garrett Air Force, Washmgton, D.C. Attorney, Agent, or Firm-Harry A. Herbert, Jr.; g. 2 David wllkmson [21] Appl. No.: 392,380 [57] ABSTRACT A solid fuel ramjet powered missile having the air inlsz] Cl gy g gg gg lets positioned adjacent the aft end of the fuel grain [5 1 1 Int Cl F02k 7/10 with a channel provided adjacent the fuel grain to pro- [58] Fieid 253 256 vide primary air into the forward end of the fuel grain 261 with the secondary air being supplied directly to the secondary combustor. A valve is provided in the pri- [56] References Cited znai'y air flow channel to control the air flow into the UNITED STATES PATENTS gram 2,977,753 4/1961 Boulet 60/270 R 2 Claims 2 Drawing Figures 1 AFT INLET RAMJET POWERED MISSILE I BACKGROUND OF THE INVENTION Solid fuel ramjet powered missiles have several advantages over liquid fuel ramjets. The fuel is safer because fuel leakage cannot occur. Also, burning is more stable since the hot fuel grain tends to stabilize combustion in the primary zone and fuel utilization automatically responds to changes in altitude and velocity. In prior art solid fuel ramjet powered missiles, the engine air inlet is placed forward of the forward end of the fuel grain with bypass channels being provided to channel air to the secondary combustor as in the US. Pat. to Chandler No. 2,799,987. Since the primary air flow is normally only a small percentage of the total flow, large ducts are required to supply the major portion of the air to the secondary combustor. Also, since the rate of burning of the fuel grain is a function of the exposed area, either the fuel grain has to be specially designed to provide a uniform burning rate or an uneven burning rate with poor thrust control will result.

BRIEF SUMMARY OF THE INVENTION According to this invention, the air inlets are positioned near the aft end of the fuel grain to provide increased missile stability since the static aerodynamic stability of the missile is reduced as the inlets are moved forward. With the aft inlets, the large air flow is directly into the secondary combustor which reduces pipe flow losses. Also, since the primary air flow is normally much less than the secondary air flow, a smaller size duct can be used for primary air flow thus reducing the overall weight of the missile. A flow control valve is provided in the primary air flow channel so that the burning rate of the fuel grain can be controlled.

IN THE DRAWING HO. 1 is a schematic partially cut away sectional view of a solid fuel ramjet according to the invention.

FIG. 2 is a sectional view of the device of H0. 1 along the line 2-2.

DETAILED DESCRlPTlON OF THE DRAWING Reference is now made to FIG. 1 of the drawing which shows a solid fuel ramjet missile having a conventional payload such as a target acquisition section 12, an ordnance section 14, a flight control section 16 and a ramjet section 18, with stabilizing fins 19 located at the aft end of the missile.

The ramjet section 18 has a solid fuel grain 20 positioned within chamber 22 with the exit nozzle 24 at the aft end of the secondary combustor 26. The solid fuel grain may be any conventional air burning fuel grain such as magnesium and aluminum with a rubber binder. For some applications, a small amount of oxidizer may be added with the amount added being insufficient to maintain combustion in the absence of air.

The ram air inlet 28 has its lip 29 positioned near the trailing end of the fuel grain with about percent of the ram air being directed into the secondary combustor 26 by flow vanes 30. A conventional boundary layer bleed is provided at 25. A small portion of the ram air, for example about l5 percent, is bled off by flow director 32 and passed along channel 34 to the forward end of the fuel grain to provide primary air for burning the fuel grain. Primary combustion occurs under fuel rich conditions in the longitudinal channel 35 through the center of the fuel grain. Fuel rich products of primary combustion are further burned in the secondary combustor 26.

Since the fuel system of the solid propellant burner is easily throttleable by throttling the primary air flow, a valve 37 is provided to control the flow of primary air into the fuel grain channel 35. The valve 37 may be positioned by a hydraulic, pneumatic or screw jack drive system 38 which may be controlled either by a command signal from the flight control section or in response to a preset program. For example, the missile could be programmed to provide a constant thrust as the area of the fuel grain changes with burning.

A conventional igniter 41, such as a pyrotechnic material ignited with squib, initiates the burning of the fuel grain in a conventional manner upon command from the flight control section, through lines 43, which may also carry the control signal to fins 19.

Though not shown, the missile can be adapted for use with a rocket-ramjet engine by providing a rocket fuel grain in chamber 26 and configuring nozzle 24 for hybrid operation in a conventional manner.

While only one inlet scoop and one primary air channel are shown, more than one may be provided if desired.

There is thus provided a solid fuel ramjet powered missile with increased static stability, lower inlet air pipe flow losses and a controlled burning rate.

I claim:

1. in a solid fuel ramjet powered missile, having a pay-load section and a ramjet section including a fuel grain with an air passage therethrough and means for igniting the fuel grain; a secondary combustor positioned at the aft end of the fuel grain; apparatus for supplying air to said fuel grain and said secondary combustor comprising; an air inlet having its lip positioned near the aft end of said fuel grain; means within said inlet for directing a major portion of the air, entering the inlet, into the secondary combustor; a channel adjacent the fuel grain, extending from said inlet to a position adjacent the forward end of the fuel grain, for providing primary air to the forward end of the fuel grain.

the flow of air into the fuel grain. 

1. In a solid fuel ramjet powered missile, having a pay-load section and a ramjet section including a fuel grain with an air passage therethrough and means for igniting the fuel grain; a secondary combustor positioned at the aft end of the fuel grain; apparatus for supplying air to said fuel grain and said secondary combustor comprising; an air inlet having its lip positioned near the aft end of said fuel grain; means within said inlet for directing a major portion of the air, entering the inlet, into the secondary combustor; a channel adjacent the fuel grain, extending from said inlet to a position adjacent the forward end of the fuel grain, for providing primary air to the forward end of the fuel grain.
 2. The device as recited in claim 1 wherein said missile includes a flight control section; means responsive to a signal from the flight control section for controlling the flow of air into the fuel grain. 